1. Field of the Invention
This invention relates to methods for treating seismic data in a manner to account for severely alias events. The methods are directed generally to interpolation techniques which in the presence of aliased events enable the production of high resolution data in preparation of the data for multi-trace processing and more specifically for migration.
2. Description of the Prior Art
The proper choice of spatial sampling interval is of significant importance in the design of seismic data acquisition techniques. Too large a sampling interval has a negative effect upon multi-trace processing of seismic data, especially migration since the sampling theorem is violated. Poor results are obtained when the spatial sampling interval is too large. On the other hand, too small a sampling interval in the field adds significantly to the cost of seismic data acquisition particularly in the 3-dimensional (3-D) case. Economic benefits can be obtained by interpolating aliased seismic data. This reduces the cost of data acquisition and prepares the data for improved multi-trace processing.
The effect of interpolating spatially aliased seismic data is dramatically illustrated in FIGS. 4 and 5 of paper entitled Trace Interpolation in Seismic Data Processing by V. Bardon appearing in Geophysical Prospecting 35 pages 343-358 published in 1987. It is obvious from an examination of those figures that migration of spatially aliased data produces useless results.
A number of interpolation techniques are available, among them being sinc interpolation. However, these techniques are inadequate in the processing of spatially aliased events to provide data suitable for migration and other multi-trace processes. Other interpolation techniques have been proposed among them being a technique which searches mult-trace data in the X-t space for the locally most coherent dip and interpolates amplitude along the dip direction. However, this technique, since it only takes in account the most coherent dip, fails to provide the resolution necessary for an accurate interpretation of the migrated data.
The present invention produces high resolution sections free of aliasing by following a two step procedure. The first step involves a data adaptive procedure for picking dips in small overlapping spatio-temporal gates. The second step utilizes the dips to perform a localized wave field decomposition of the dipping events. The aliased events are interpolated along their true dip directions onto the interpolated trace positions using time shifting operations. By separating the data into the aliased and non-aliased segments the non-aliased or un-aliased events may be processed with the conventional sinc interpolation and then combined with the results of the two step procedure of the present invention.